Source/portable/IAR/ARM_CM0/port.c - third_party/github/STMicroelectronics/stm32_mw_freertos - Git at Google

 /*
  * FreeRTOS Kernel V10.2.1
  * Copyright (C) 2019 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of
  * this software and associated documentation files (the "Software"), to deal in
  * the Software without restriction, including without limitation the rights to
  * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
  * the Software, and to permit persons to whom the Software is furnished to do so,
  * subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in all
  * copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
  * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
  * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
  * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  *
  * http://www.FreeRTOS.org
  * http://aws.amazon.com/freertos
  *
  * 1 tab == 4 spaces!
  */

 /*-----------------------------------------------------------
  * Implementation of functions defined in portable.h for the ARM CM0 port.
  *----------------------------------------------------------*/

 /* IAR includes. */
 #include "intrinsics.h"

 /* Scheduler includes. */
 #include "FreeRTOS.h"
 #include "task.h"

 #ifndef configSYSTICK_CLOCK_HZ
 	#define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
 #endif

 /* Constants required to manipulate the NVIC. */
 /* Constants required to manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL                  ( * ( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD                  ( * ( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE         ( * ( ( volatile uint32_t * ) 0xe000e018 ) )
 #define portNVIC_SYSPRI2                       ( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
 #define portNVIC_SYSTICK_CLK		0x00000004
 #define portNVIC_SYSTICK_INT		0x00000002
 #define portNVIC_SYSTICK_ENABLE		0x00000001
 #define portNVIC_SYSTICK_COUNT_FLAG		( 1UL << 16UL )
 #define portMIN_INTERRUPT_PRIORITY	( 255UL )
 #define portNVIC_PENDSV_PRI			( portMIN_INTERRUPT_PRIORITY << 16UL )
 #define portNVIC_SYSTICK_PRI		( portMIN_INTERRUPT_PRIORITY << 24UL )

 /* Constants required to set up the initial stack. */
 #define portINITIAL_XPSR			( 0x01000000 )

 /* For backward compatibility, ensure configKERNEL_INTERRUPT_PRIORITY is
 defined.  The value 255 should also ensure backward compatibility.
 FreeRTOS.org versions prior to V4.3.0 did not include this definition. */
 #ifndef configKERNEL_INTERRUPT_PRIORITY
 	#define configKERNEL_INTERRUPT_PRIORITY 0
 #endif

 /* The systick is a 24-bit counter. */
 #define portMAX_24_BIT_NUMBER				( 0xffffffUL )

 /* A fiddle factor to estimate the number of SysTick counts that would have
 occurred while the SysTick counter is stopped during tickless idle
 calculations. */
 #define portMISSED_COUNTS_FACTOR			( 45UL )

 /* Each task maintains its own interrupt status in the critical nesting
 variable. */
 static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;

 /*
  * Setup the timer to generate the tick interrupts.
  */
 static void prvSetupTimerInterrupt( void );

 /*
  * Exception handlers.
  */
 void xPortSysTickHandler( void );

 /*
  * Start first task is a separate function so it can be tested in isolation.
  */
 extern void vPortStartFirstTask( void );

 /*
  * Used to catch tasks that attempt to return from their implementing function.
  */
 static void prvTaskExitError( void );

 /*-----------------------------------------------------------*/

 /*
  * The number of SysTick increments that make up one tick period.
  */
 #if configUSE_TICKLESS_IDLE == 1
 	static unsigned long ulTimerCountsForOneTick = 0;
 #endif /* configUSE_TICKLESS_IDLE */

 /*
  * The maximum number of tick periods that can be suppressed is limited by the
  * 24 bit resolution of the SysTick timer.
  */
 #if configUSE_TICKLESS_IDLE == 1
 	static unsigned long xMaximumPossibleSuppressedTicks = 0;
 #endif /* configUSE_TICKLESS_IDLE */

 /*
  * Compensate for the CPU cycles that pass while the SysTick is stopped (low
  * power functionality only.
  */
 #if configUSE_TICKLESS_IDLE == 1
 	static unsigned long ulStoppedTimerCompensation = 0;
 #endif /* configUSE_TICKLESS_IDLE */

 /*
  * See header file for description.
  */
 StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
 {
 	/* Simulate the stack frame as it would be created by a context switch
 	interrupt. */
 	pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
 	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
 	pxTopOfStack--;
 	*pxTopOfStack = ( StackType_t ) pxCode;	/* PC */
 	pxTopOfStack--;
 	*pxTopOfStack = ( StackType_t ) prvTaskExitError;	/* LR */
 	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
 	*pxTopOfStack = ( StackType_t ) pvParameters;	/* R0 */
 	pxTopOfStack -= 8; /* R11..R4. */

 	return pxTopOfStack;
 }
 /*-----------------------------------------------------------*/

 static void prvTaskExitError( void )
 {
 	/* A function that implements a task must not exit or attempt to return to
 	its caller as there is nothing to return to.  If a task wants to exit it
 	should instead call vTaskDelete( NULL ).

 	Artificially force an assert() to be triggered if configASSERT() is
 	defined, then stop here so application writers can catch the error. */
 	configASSERT( uxCriticalNesting == ~0UL );
 	portDISABLE_INTERRUPTS();
 	for( ;; );
 }
 /*-----------------------------------------------------------*/

 /*
  * See header file for description.
  */
 BaseType_t xPortStartScheduler( void )
 {
 	/* Make PendSV and SysTick the lowest priority interrupts. */
 	portNVIC_SYSPRI2 |= portNVIC_PENDSV_PRI;
 	portNVIC_SYSPRI2 |= portNVIC_SYSTICK_PRI;

 	/* Start the timer that generates the tick ISR.  Interrupts are disabled
 	here already. */
 	prvSetupTimerInterrupt();

 	/* Initialise the critical nesting count ready for the first task. */
 	uxCriticalNesting = 0;

 	/* Start the first task. */
 	vPortStartFirstTask();

 	/* Should not get here! */
 	return 0;
 }
 /*-----------------------------------------------------------*/

 void vPortEndScheduler( void )
 {
 	/* Not implemented in ports where there is nothing to return to.
 	Artificially force an assert. */
 	configASSERT( uxCriticalNesting == 1000UL );
 }
 /*-----------------------------------------------------------*/

 void vPortYield( void )
 {
 	/* Set a PendSV to request a context switch. */
 	*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;

 	/* Barriers are normally not required but do ensure the code is completely
 	within the specified behaviour for the architecture. */
 	__DSB();
 	__ISB();
 }
 /*-----------------------------------------------------------*/

 void vPortEnterCritical( void )
 {
 	portDISABLE_INTERRUPTS();
 	uxCriticalNesting++;
 	__DSB();
 	__ISB();
 }
 /*-----------------------------------------------------------*/

 void vPortExitCritical( void )
 {
 	configASSERT( uxCriticalNesting );
 	uxCriticalNesting--;
 	if( uxCriticalNesting == 0 )
 	{
 		portENABLE_INTERRUPTS();
 	}
 }
 /*-----------------------------------------------------------*/

 void xPortSysTickHandler( void )
 {
 uint32_t ulPreviousMask;

 	ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
 	{
 		/* Increment the RTOS tick. */
 		if( xTaskIncrementTick() != pdFALSE )
 		{
 			/* Pend a context switch. */
 			*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;
 		}
 	}
 	portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
 }
 /*-----------------------------------------------------------*/

 #if configUSE_TICKLESS_IDLE == 1

 	__weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
 	{
 	uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;
 	TickType_t xModifiableIdleTime;

 		/* Make sure the SysTick reload value does not overflow the counter. */
 		if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
 		{
 			xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
 		}

 		/* Stop the SysTick momentarily.  The time the SysTick is stopped for
 		is accounted for as best it can be, but using the tickless mode will
 		inevitably result in some tiny drift of the time maintained by the
 		kernel with respect to calendar time. */
 		portNVIC_SYSTICK_CTRL &= ~portNVIC_SYSTICK_ENABLE;

 		/* Calculate the reload value required to wait xExpectedIdleTime
 		tick periods.  -1 is used because this code will execute part way
 		through one of the tick periods. */
 		ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
 		if( ulReloadValue > ulStoppedTimerCompensation )
 		{
 			ulReloadValue -= ulStoppedTimerCompensation;
 		}

 		/* Enter a critical section but don't use the taskENTER_CRITICAL()
 		method as that will mask interrupts that should exit sleep mode. */
 		__disable_interrupt();

 		/* If a context switch is pending or a task is waiting for the scheduler
 		to be unsuspended then abandon the low power entry. */
 		if( eTaskConfirmSleepModeStatus() == eAbortSleep )
 		{
 			/* Restart from whatever is left in the count register to complete
 			this tick period. */
 			portNVIC_SYSTICK_LOAD = portNVIC_SYSTICK_CURRENT_VALUE;

 			/* Restart SysTick. */
 			portNVIC_SYSTICK_CTRL |= portNVIC_SYSTICK_ENABLE;

 			/* Reset the reload register to the value required for normal tick
 			periods. */
 			portNVIC_SYSTICK_LOAD = ulTimerCountsForOneTick - 1UL;

 			/* Re-enable interrupts - see comments above __disable_interrupt()
 			call above. */
 			__enable_interrupt();
 		}
 		else
 		{
 			/* Set the new reload value. */
 			portNVIC_SYSTICK_LOAD = ulReloadValue;

 			/* Clear the SysTick count flag and set the count value back to
 			zero. */
 			portNVIC_SYSTICK_CURRENT_VALUE = 0UL;

 			/* Restart SysTick. */
 			portNVIC_SYSTICK_CTRL |= portNVIC_SYSTICK_ENABLE;

 			/* Sleep until something happens.  configPRE_SLEEP_PROCESSING() can
 			set its parameter to 0 to indicate that its implementation contains
 			its own wait for interrupt or wait for event instruction, and so wfi
 			should not be executed again.  However, the original expected idle
 			time variable must remain unmodified, so a copy is taken. */
 			xModifiableIdleTime = xExpectedIdleTime;
 			configPRE_SLEEP_PROCESSING( &xModifiableIdleTime );
 			if( xModifiableIdleTime > 0 )
 			{
 				__DSB();
 				__WFI();
 				__ISB();
 			}
 			configPOST_SLEEP_PROCESSING( &xExpectedIdleTime );

 			/* Stop SysTick.  Again, the time the SysTick is stopped for is
 			accounted for as best it can be, but using the tickless mode will
 			inevitably result in some tiny drift of the time maintained by the
 			kernel with respect to calendar time. */
 			ulSysTickCTRL = portNVIC_SYSTICK_CTRL;
 			portNVIC_SYSTICK_CTRL = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE );

 			/* Re-enable interrupts - see comments above __disable_interrupt()
 			call above. */
 			__enable_interrupt();

 			if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG ) != 0 )
 			{
 				uint32_t ulCalculatedLoadValue;

 				/* The tick interrupt has already executed, and the SysTick
 				count reloaded with ulReloadValue.  Reset the
 				portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
 				period. */
 				ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE );

 				/* Don't allow a tiny value, or values that have somehow
 				underflowed because the post sleep hook did something
 				that took too long. */
 				if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
 				{
 					ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
 				}

 				portNVIC_SYSTICK_LOAD = ulCalculatedLoadValue;

 				/* The tick interrupt handler will already have pended the tick
 				processing in the kernel.  As the pending tick will be
 				processed as soon as this function exits, the tick value
 				maintained by the tick is stepped forward by one less than the
 				time spent waiting. */
 				ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
 			}
 			else
 			{
 				/* Something other than the tick interrupt ended the sleep.
 				Work out how long the sleep lasted rounded to complete tick
 				periods (not the ulReload value which accounted for part
 				ticks). */
 				ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE;

 				/* How many complete tick periods passed while the processor
 				was waiting? */
 				ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;

 				/* The reload value is set to whatever fraction of a single tick
 				period remains. */
 				portNVIC_SYSTICK_LOAD = ( ( ulCompleteTickPeriods + 1 ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
 			}

 			/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
 			again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
 			value.  The critical section is used to ensure the tick interrupt
 			can only execute once in the case that the reload register is near
 			zero. */
 			portNVIC_SYSTICK_CURRENT_VALUE = 0UL;
 			portENTER_CRITICAL();
 			{
 				portNVIC_SYSTICK_CTRL |= portNVIC_SYSTICK_ENABLE;
 				vTaskStepTick( ulCompleteTickPeriods );
 				portNVIC_SYSTICK_LOAD = ulTimerCountsForOneTick - 1UL;
 			}
 			portEXIT_CRITICAL();
 		}
 	}

 #endif /* #if configUSE_TICKLESS_IDLE */
 /*-----------------------------------------------------------*/

 /*
  * Setup the systick timer to generate the tick interrupts at the required
  * frequency.
  */
 static void prvSetupTimerInterrupt( void )
 {
 	/* Calculate the constants required to configure the tick interrupt. */
 	#if configUSE_TICKLESS_IDLE == 1
 	{
 		ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
 		xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
 		ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
 	}
 	#endif /* configUSE_TICKLESS_IDLE */

 	/* Stop and reset the SysTick. */
 	portNVIC_SYSTICK_CTRL = 0UL;
 	portNVIC_SYSTICK_CURRENT_VALUE = 0UL;

 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;
 }
 /*-----------------------------------------------------------*/
	/*
	* FreeRTOS Kernel V10.2.1
	* Copyright (C) 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy of
	* this software and associated documentation files (the "Software"), to deal in
	* the Software without restriction, including without limitation the rights to
	* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
	* the Software, and to permit persons to whom the Software is furnished to do so,
	* subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in all
	* copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
	* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
	* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
	* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
	* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
	*
	* http://www.FreeRTOS.org
	* http://aws.amazon.com/freertos
	*
	* 1 tab == 4 spaces!
	*/

	/*-----------------------------------------------------------
	* Implementation of functions defined in portable.h for the ARM CM0 port.
	----------------------------------------------------------/

	/* IAR includes. */
	#include "intrinsics.h"

	/* Scheduler includes. */
	#include "FreeRTOS.h"
	#include "task.h"

	#ifndef configSYSTICK_CLOCK_HZ
	#define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
	#endif

	/* Constants required to manipulate the NVIC. */
	/* Constants required to manipulate the NVIC. */
	#define portNVIC_SYSTICK_CTRL ( * ( ( volatile uint32_t * ) 0xe000e010 ) )
	#define portNVIC_SYSTICK_LOAD ( * ( ( volatile uint32_t * ) 0xe000e014 ) )
	#define portNVIC_SYSTICK_CURRENT_VALUE ( * ( ( volatile uint32_t * ) 0xe000e018 ) )
	#define portNVIC_SYSPRI2 ( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
	#define portNVIC_SYSTICK_CLK 0x00000004
	#define portNVIC_SYSTICK_INT 0x00000002
	#define portNVIC_SYSTICK_ENABLE 0x00000001
	#define portNVIC_SYSTICK_COUNT_FLAG ( 1UL << 16UL )
	#define portMIN_INTERRUPT_PRIORITY ( 255UL )
	#define portNVIC_PENDSV_PRI ( portMIN_INTERRUPT_PRIORITY << 16UL )
	#define portNVIC_SYSTICK_PRI ( portMIN_INTERRUPT_PRIORITY << 24UL )

	/* Constants required to set up the initial stack. */
	#define portINITIAL_XPSR ( 0x01000000 )

	/* For backward compatibility, ensure configKERNEL_INTERRUPT_PRIORITY is
	defined. The value 255 should also ensure backward compatibility.
	FreeRTOS.org versions prior to V4.3.0 did not include this definition. */
	#ifndef configKERNEL_INTERRUPT_PRIORITY
	#define configKERNEL_INTERRUPT_PRIORITY 0
	#endif

	/* The systick is a 24-bit counter. */
	#define portMAX_24_BIT_NUMBER ( 0xffffffUL )

	/* A fiddle factor to estimate the number of SysTick counts that would have
	occurred while the SysTick counter is stopped during tickless idle
	calculations. */
	#define portMISSED_COUNTS_FACTOR ( 45UL )

	/* Each task maintains its own interrupt status in the critical nesting
	variable. */
	static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;

	/*
	* Setup the timer to generate the tick interrupts.
	*/
	static void prvSetupTimerInterrupt( void );

	/*
	* Exception handlers.
	*/
	void xPortSysTickHandler( void );

	/*
	* Start first task is a separate function so it can be tested in isolation.
	*/
	extern void vPortStartFirstTask( void );

	/*
	* Used to catch tasks that attempt to return from their implementing function.
	*/
	static void prvTaskExitError( void );

	/-----------------------------------------------------------/

	/*
	* The number of SysTick increments that make up one tick period.
	*/
	#if configUSE_TICKLESS_IDLE == 1
	static unsigned long ulTimerCountsForOneTick = 0;
	#endif /* configUSE_TICKLESS_IDLE */

	/*
	* The maximum number of tick periods that can be suppressed is limited by the
	* 24 bit resolution of the SysTick timer.
	*/
	#if configUSE_TICKLESS_IDLE == 1
	static unsigned long xMaximumPossibleSuppressedTicks = 0;
	#endif /* configUSE_TICKLESS_IDLE */

	/*
	* Compensate for the CPU cycles that pass while the SysTick is stopped (low
	* power functionality only.
	*/
	#if configUSE_TICKLESS_IDLE == 1
	static unsigned long ulStoppedTimerCompensation = 0;
	#endif /* configUSE_TICKLESS_IDLE */

	/*
	* See header file for description.
	*/
	StackType_t pxPortInitialiseStack( StackType_t pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
	{
	/* Simulate the stack frame as it would be created by a context switch
	interrupt. */
	pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
	pxTopOfStack = portINITIAL_XPSR; / xPSR */
	pxTopOfStack--;
	pxTopOfStack = ( StackType_t ) pxCode; / PC */
	pxTopOfStack--;
	pxTopOfStack = ( StackType_t ) prvTaskExitError; / LR */
	pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
	pxTopOfStack = ( StackType_t ) pvParameters; / R0 */
	pxTopOfStack -= 8; /* R11..R4. */

	return pxTopOfStack;
	}
	/-----------------------------------------------------------/

	static void prvTaskExitError( void )
	{
	/* A function that implements a task must not exit or attempt to return to
	its caller as there is nothing to return to. If a task wants to exit it
	should instead call vTaskDelete( NULL ).

	Artificially force an assert() to be triggered if configASSERT() is
	defined, then stop here so application writers can catch the error. */
	configASSERT( uxCriticalNesting == ~0UL );
	portDISABLE_INTERRUPTS();
	for( ;; );
	}
	/-----------------------------------------------------------/

	/*
	* See header file for description.
	*/
	BaseType_t xPortStartScheduler( void )
	{
	/* Make PendSV and SysTick the lowest priority interrupts. */
	portNVIC_SYSPRI2 \|= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2 \|= portNVIC_SYSTICK_PRI;

	/* Start the timer that generates the tick ISR. Interrupts are disabled
	here already. */
	prvSetupTimerInterrupt();

	/* Initialise the critical nesting count ready for the first task. */
	uxCriticalNesting = 0;

	/* Start the first task. */
	vPortStartFirstTask();

	/* Should not get here! */
	return 0;
	}
	/-----------------------------------------------------------/

	void vPortEndScheduler( void )
	{
	/* Not implemented in ports where there is nothing to return to.
	Artificially force an assert. */
	configASSERT( uxCriticalNesting == 1000UL );
	}
	/-----------------------------------------------------------/

	void vPortYield( void )
	{
	/* Set a PendSV to request a context switch. */
	*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;

	/* Barriers are normally not required but do ensure the code is completely
	within the specified behaviour for the architecture. */
	__DSB();
	__ISB();
	}
	/-----------------------------------------------------------/

	void vPortEnterCritical( void )
	{
	portDISABLE_INTERRUPTS();
	uxCriticalNesting++;
	__DSB();
	__ISB();
	}
	/-----------------------------------------------------------/

	void vPortExitCritical( void )
	{
	configASSERT( uxCriticalNesting );
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
	portENABLE_INTERRUPTS();
	}
	}
	/-----------------------------------------------------------/

	void xPortSysTickHandler( void )
	{
	uint32_t ulPreviousMask;

	ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
	{
	/* Increment the RTOS tick. */
	if( xTaskIncrementTick() != pdFALSE )
	{
	/* Pend a context switch. */
	*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;
	}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
	}
	/-----------------------------------------------------------/

	#if configUSE_TICKLESS_IDLE == 1

	__weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
	{
	uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;
	TickType_t xModifiableIdleTime;

	/* Make sure the SysTick reload value does not overflow the counter. */
	if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
	{
	xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
	}

	/* Stop the SysTick momentarily. The time the SysTick is stopped for
	is accounted for as best it can be, but using the tickless mode will
	inevitably result in some tiny drift of the time maintained by the
	kernel with respect to calendar time. */
	portNVIC_SYSTICK_CTRL &= ~portNVIC_SYSTICK_ENABLE;

	/* Calculate the reload value required to wait xExpectedIdleTime
	tick periods. -1 is used because this code will execute part way
	through one of the tick periods. */
	ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
	if( ulReloadValue > ulStoppedTimerCompensation )
	{
	ulReloadValue -= ulStoppedTimerCompensation;
	}

	/* Enter a critical section but don't use the taskENTER_CRITICAL()
	method as that will mask interrupts that should exit sleep mode. */
	__disable_interrupt();

	/* If a context switch is pending or a task is waiting for the scheduler
	to be unsuspended then abandon the low power entry. */
	if( eTaskConfirmSleepModeStatus() == eAbortSleep )
	{
	/* Restart from whatever is left in the count register to complete
	this tick period. */
	portNVIC_SYSTICK_LOAD = portNVIC_SYSTICK_CURRENT_VALUE;

	/* Restart SysTick. */
	portNVIC_SYSTICK_CTRL \|= portNVIC_SYSTICK_ENABLE;

	/* Reset the reload register to the value required for normal tick
	periods. */
	portNVIC_SYSTICK_LOAD = ulTimerCountsForOneTick - 1UL;

	/* Re-enable interrupts - see comments above __disable_interrupt()
	call above. */
	__enable_interrupt();
	}
	else
	{
	/* Set the new reload value. */
	portNVIC_SYSTICK_LOAD = ulReloadValue;

	/* Clear the SysTick count flag and set the count value back to
	zero. */
	portNVIC_SYSTICK_CURRENT_VALUE = 0UL;

	/* Restart SysTick. */
	portNVIC_SYSTICK_CTRL \|= portNVIC_SYSTICK_ENABLE;

	/* Sleep until something happens. configPRE_SLEEP_PROCESSING() can
	set its parameter to 0 to indicate that its implementation contains
	its own wait for interrupt or wait for event instruction, and so wfi
	should not be executed again. However, the original expected idle
	time variable must remain unmodified, so a copy is taken. */
	xModifiableIdleTime = xExpectedIdleTime;
	configPRE_SLEEP_PROCESSING( &xModifiableIdleTime );
	if( xModifiableIdleTime > 0 )
	{
	__DSB();
	__WFI();
	__ISB();
	}
	configPOST_SLEEP_PROCESSING( &xExpectedIdleTime );

	/* Stop SysTick. Again, the time the SysTick is stopped for is
	accounted for as best it can be, but using the tickless mode will
	inevitably result in some tiny drift of the time maintained by the
	kernel with respect to calendar time. */
	ulSysTickCTRL = portNVIC_SYSTICK_CTRL;
	portNVIC_SYSTICK_CTRL = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE );

	/* Re-enable interrupts - see comments above __disable_interrupt()
	call above. */
	__enable_interrupt();

	if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG ) != 0 )
	{
	uint32_t ulCalculatedLoadValue;

	/* The tick interrupt has already executed, and the SysTick
	count reloaded with ulReloadValue. Reset the
	portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
	period. */
	ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE );

	/* Don't allow a tiny value, or values that have somehow
	underflowed because the post sleep hook did something
	that took too long. */
	if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) \|\| ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
	{
	ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
	}

	portNVIC_SYSTICK_LOAD = ulCalculatedLoadValue;

	/* The tick interrupt handler will already have pended the tick
	processing in the kernel. As the pending tick will be
	processed as soon as this function exits, the tick value
	maintained by the tick is stepped forward by one less than the
	time spent waiting. */
	ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
	}
	else
	{
	/* Something other than the tick interrupt ended the sleep.
	Work out how long the sleep lasted rounded to complete tick
	periods (not the ulReload value which accounted for part
	ticks). */
	ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE;

	/* How many complete tick periods passed while the processor
	was waiting? */
	ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;

	/* The reload value is set to whatever fraction of a single tick
	period remains. */
	portNVIC_SYSTICK_LOAD = ( ( ulCompleteTickPeriods + 1 ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
	}

	/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
	again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
	value. The critical section is used to ensure the tick interrupt
	can only execute once in the case that the reload register is near
	zero. */
	portNVIC_SYSTICK_CURRENT_VALUE = 0UL;
	portENTER_CRITICAL();
	{
	portNVIC_SYSTICK_CTRL \|= portNVIC_SYSTICK_ENABLE;
	vTaskStepTick( ulCompleteTickPeriods );
	portNVIC_SYSTICK_LOAD = ulTimerCountsForOneTick - 1UL;
	}
	portEXIT_CRITICAL();
	}
	}

	#endif /* #if configUSE_TICKLESS_IDLE */
	/-----------------------------------------------------------/

	/*
	* Setup the systick timer to generate the tick interrupts at the required
	* frequency.
	*/
	static void prvSetupTimerInterrupt( void )
	{
	/* Calculate the constants required to configure the tick interrupt. */
	#if configUSE_TICKLESS_IDLE == 1
	{
	ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
	xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
	ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
	}
	#endif /* configUSE_TICKLESS_IDLE */

	/* Stop and reset the SysTick. */
	portNVIC_SYSTICK_CTRL = 0UL;
	portNVIC_SYSTICK_CURRENT_VALUE = 0UL;

	/* Configure SysTick to interrupt at the requested rate. */
	portNVIC_SYSTICK_LOAD = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
	portNVIC_SYSTICK_CTRL = portNVIC_SYSTICK_CLK \| portNVIC_SYSTICK_INT \| portNVIC_SYSTICK_ENABLE;
	}
	/-----------------------------------------------------------/